1. Field of the Invention
This invention is directed to methods for annealing a substrate using a pulse of particles such as electrons, protons, ions, or other, neutral particles. The invention is also directed to integrated devices or circuits made by such methods. The substrate can be composed of silicon, gallium arsenide, or other semiconductor species, or can include an insulative material with a relatively thin-film of semiconductor material formed thereon. The apparatus and methods can be used to anneal or activate integrated devices or circuits formed in the substrate, and to form low-resistance suicide regions thereon. Such integrated devices can include active devices such as transistors or diodes, or passive devices such as resistors or capacitors. For example, the apparatus and method can be used to anneal a substrate to obtain a relatively high crystalline state therein, or to activate the substrate to incorporate dopant atoms into the substrate""s crystalline lattice, to achieve proper electrical performance of the integrated devices.
2. Description of the Related Art
In forming integrated devices in a semiconductor substrate it is common to use ion implantation to introduce dopant atoms of appropriate species into the substrate to form n-type or p-type regions. Immediately after implantation the dopant atoms are not generally positioned within the substrate where they can be useful to achieve proper electrical performance of the integrated device being formed. Also, the dopant atoms are accelerated to relatively high-energies by ion implanters. Therefore, upon colliding with the substrate the dopant atoms cause considerable damage to the substrate by breaking chemical bonds therein. The crystalline structure of the substrate must be restored, and the dopant atoms incorporated into it, in order to obtain proper electrical performance of the integrated devices. Annealing is typically performed by heating the substrate so that the dopant atoms and substrate atoms have sufficient energy to realign. Of considerable importance in the manufacture of integrated devices or circuits is the xe2x80x9cthroughputxe2x80x9d that a manufacturer can obtain with a process for forming integrated devices, and the cost necessary to achieve that throughput. It is always desirable to reduce the number of steps in a process for forming an integrated device or circuit as long as the integrated circuits or devices suffer no significant degradation in performance as a result thereof. Of course, a process that not only reduces the number of steps required to form an integrated device or circuit, but also increases its electrical performance, would be highly desirable.
In the annealing process it is desirable that the heating of the doped regions be uniform so that all regions are annealed similarly and so perform similarly. An annealing process should therefore have the capability to uniformly anneal doped regions of a substrate.
Another problem related to annealing is the necessity to limit the diffusion of dopant atoms within the circuit. With the ongoing reduction of device dimensions over time to achieve faster switching speeds and to incorporate more devices per unit area within the substrate, it becomes increasingly important to restrict diffusion. Otherwise, the dopant atoms can create leakage paths between source, drain and/or gate regions, which either impair or destroy electrical performance of the integrated device. It would be desirable to provide a method that reduces or eliminates diffusion of the dopant atoms in a substrate.
The invented apparatus overcomes the above-stated disadvantages. A first method of this invention includes annealing at least one region of a substrate with charged particles. The charged particles can be electrons, protons, ions, alpha particles, or neutral particles. The substrate can be composed of a semiconductor material, for example. The particles can be p-type dopant atoms including boron (B), aluminum (Al), gallium (Ga), indium (In), and palladium (Pd), or n-type dopant atoms species including arsenic (As), phosphorus (P), antimony (Sb), titanium (Ti), platinum (Pt), gold (Au), and oxygen (O). The particles can be used to anneal dopant or other atoms previously implanted into the substrate. Alternatively, the species and energies of the particles can be selected so as to simultaneously implant and anneal the substrate. This alternative implementation of the method requires the particles be a dopant species because implantation and activation are performed in a single step. If no change in the electrical state of the substrate is required, the particles can include atoms with the same valency as the substrate. Such ions include one or more of carbon (C), silicon (Si), and germanium (Ge) or other species with the same valency as the substrate.
The particles can be applied to the substrate with a predetermined flux, energy, pulse duration, and dosage. The energy of the particles can be determined based upon one or more of the following criteria:
(1) the particles have an energy corresponding to an absorption length that is equal to or greater than the desired junction depth;
(2) the particle species is chosen to correspond to the desired dopant and the dose corresponds to the desired doping concentration; and
(3) the particles have an energy, flux, and pulse duration to raise the temperature of the irradiated region sufficiently high for annealing or activation to occur.
The energy of the charged particles can range from one-tenth (0.1) to one-hundred (100) kilo-electron-Volts, the range for electrons being from five (5) to seven (7) keV. The charged particle flux generally ranges from 1012 to 1018 particles per square centimeter at the surface of the substrate. The particle flux incident on the surface of the substrate can be from 5xc3x971012 to 5xc3x971013 particles per square centimeter. The pulse duration of the particles can be from 10xe2x88x929 to 104 seconds. However, within the limitations of presently available equipment, the pulse duration of the particles can be in a range from about 5xc3x9710xe2x88x927 to 104 seconds. The energy dose can be from one-tenth (0.1) to one (1.0) Joules/cm2.
The substrate can include dopants with a predetermined distribution in the substrate and the pulse duration of the particle annealing beam can be limited to prevent significant change in the dopant distribution due to diffusion. The doped region can be amorphous and the underlying substrate can be crystalline. The particle beam can produce a uniform temperature distribution in the amorphous region sufficient to promote crystallization of the amorphous region with the crystalline portion of the substrate acting as a seed crystal. A second method of the invention includes generating particles, accelerating the particles toward a substrate, and focusing the particles to increase the flux of the particles so that they have sufficient flux and energy to anneal a region of the substrate. The particles can include electrons, protons, ions, alpha particles, and other neutral atoms. As with the first method, the second method can be performed with a multicusp generator and an accelerator, and optional focusing lens and beam neutralizer. Most of these elements are contained in a conventional ion implanter. If the particles are dopant species, the energies, the flux and the pulse duration of the particle beam can be selected or arranged to provide the desired dopant concentration and distribution and, possibly, to achieve activation concurrently with irradiation.
It is an object of the invention to provide an apparatus and methods that can be used to produce an even temperature distribution within a doped region undergoing treatment.
It is an object of the invention to provide an apparatus and methods that can be used to anneal a substrate without significantly changing the dopant distribution therein.
These together with other features and advantages, which will become subsequently apparent, reside in the details of the invented apparatus and method as more fully hereinafter described and claimed, reference being made to the accompanying drawings, forming a part hereof, wherein like numerals refer to like parts throughout the several views.